"Your mouse is drinking water."
Translation:Wasza mysz pije wodę.
Myszka is a diminutive of mysz - a small/cute mouse. The computer mouse is referred to as myszka and not mysz more often than not in my experience, too.
While 'mysz' ends with a consonant, it is not masculine, it's feminine. That's an exception. There are more exceptions of course, but your first assumption should probably still be that a consonant ending makes a masculine noun.
And that assumption made me miss the sentence, haha. But it's a good way to learn it and to learn to be more careful.
I always fail to understand these stuff you talk above ,should i start learning from a book?
There seems to be a trap in this exercise. Most of these "pick the correct translation from the three sentences" have a pair involving the two forms of "you". In this case, however, the "twoja" sentence is incorrect as the verb has the wrong form. Just sayin'.
We don't put the 'wrong' answers, they are created by some algorithm. I guess I'd also automatically check 'twoja'.
For some reason only "wasza mysz pije wodę" was the best answer, with "twoja" only accepted. Now both will be 'best', so both will be needed in that exercise.
Ah! But I hope that, in the "twoja" version, you also fixed the "piję" to "pije" :-) .